Power problem 2.5 1999 boxster
 

Power problem

I got my car back 4 weeks ago after undergoing head gasket replacement
Since then I have had a power problem which is more noticeable the harder i try to drive the car. Up to 2.5-3k rpm I see maybe 25% drop in power, from 3k – 5k maybe up to 40% power loss. I will not take it up any further as I am a bit worried?
There is no other visible or physical signs only holding back
Anyone help?

Jason

double check cam timing and anything else that was touched from the head gasket change

check compression and compare numbers

The mechanic dealing with this is reputable but he is still not sure what it is, there are no faults showing on the readout?